<!doctype html>
<html lang="en" xmlns:v-bind="http://www.w3.org/1999/xhtml" xmlns:v-on="http://www.w3.org/1999/xhtml">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
</head>
<body>
<div id="app">
    <p><a v-bind:href="url">{{url}}</a></p>
    <button v-on:click="add(2)">{{number}}</button>
</div>
</body>
<script src="../../vender/vue@2.4.2.js"></script>
<script>

    var vm=new Vue({
        el:'#app',
        data:{
            url:'www.vue.js',
            number:1
        },
        methods:{
            add:function(n=0){
                console.log('number:',this.number+=2);
            }
        }
    });

</script>
</html>